<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <script>

        var s = new Set()

        s.add(10)
        s.add(20)
        s.delete(10)
        console.log(s)
        console.log(s.has(20))
    </script>
</body>
</html>